Papers by Author: Yao Hui Lv

Abstract: With considering the Marangoni convection in the molten pool on plasma direct metal forming process, a finite element model posed to describe and reflect the flow in the molten pool. Results of temperature distribution modeling prepared by plasma direct metal forming process of metal powders in an Ar environment were numerically obtained and compared with experimental data. Powders of Fe314 and base plates of R235 steel were taken as sample materials. In the experiment a multi-stream nozzle capable of delivering metal powder coaxially with the plasma arc was used. The model revealed that the velosity of the front part of the pool is a little slower than aft part. Marangoni convection reinforced the convection and enhanced the heat transfer. Profile of the model is the same as the experimental data. This allows us to conclude that the model can be applied for preselecting the process parameters. Keywords: plasma, rapid forming, temperature field, Marangoni convection.

Abstract: An acrylate emulsion was modified by vinyltriethoxy silane (VTES, trade name A-151) to synthesize the acrylosilane emulsion with high properties. The effect of the amount of A-151 on the properties pf the emulsion was investigated. It found that adding 6 % of A-151, the fraction extensibility of the emulsion film could be increased to 530 % and its water absorption was reduced to 4.2 % while adding 10 % of A-151. On the other side, the particle size and distribution of the emulsion were analyzed by Scanning Electron Microscopy (SEM) and Malvern Particle Size Analyzer (PSA) respectively. The measuring results showed that the particle diameter of the modified emulsion could be between 100 and 700 nanometers, and the properties of the emulsion could be apparently improved by adding A-151 into the system of emulsion polymerization.

Abstract: Microstructure and properties of Ni-base coatings obtained by micro-plasma arc cladding was investigated. A uniform clad coating was obtained after optimizing the cladding parameters by using NiCrBSi powder. Microstructure of the coatings observed by optical and scanning electron microscopy (SEM) indicated a homogenized microstructure. It has no evident heat-affected zone and no porosity. The phase of the coating was formed by γ-N solid solution, nickel boride Ni3B, carbide Cr21.34Fe1.66C6 and Cr2B3 type chromium boride. Although it likes the laser cladding coatings, micro-plasma coatings has its own characteristic. In addition, the average microhardness and nanohardness of coatings which were much higher than the substrate were observed, and the distribution of the microhardness was drawn.

Abstract: Surface of gear that works continuously tends to be wore. Hardfacing on worn gear can repair its worn surface, restore its precision, consolidate its surface property, and save cost. Micro-Plasma Arc Welding (micro-PAW) has low heat input and narrow heat-affected zone, and it has good properties of energy concentration and high energy density. Therefore, hardfacing by micro-PAW is an effective method to repair worn gear surface. KF-Ni60A Ni-based alloy powder has good weldability property, and KF-Ni60A welding layer has low friction coefficient and good property of wear resistance between metallic hard surface, so it is a kind of good overlaying material that can be applied to the welding process to repair the worn gear surface. In this research, the method of overlaying on worn gear using KF-Ni60A Ni-based alloy powder by micro-PAW is studied. The microstructure of deposition layer and the elementary distribution of cross-section are analyzed, the surface hardness and wear resistant property of the layer are measured. The result indicates that the deposition layer and the base metal bond well, the layer has high adhesive strength and hardness, low porosity, and good property of wear resistance.

Abstract: The micro-plasma arc welding technology（MPAW） was used to remanufacture the exhaust valve of W615 engine. The ST6 Co alloy powder was selected as overlaying material, the processing parameters of overlaying was optimized considering the geometry demand of deposited layer, and the current downslope method was adopted to weaken the arc crater. The microstructure characteristics and the micro-hardness of the weld were investigated, no defects were found in the deposited layer or at the interface, and the heat-affected zone among joint was not evident. The maximum hardness situated at the top layer being 657.8HV, with a slight decrease towards the bottom layer and fusion zone.

Abstract: The thrust surface of W615 engine is remanufactured by plasma transferred arc (PTA) powder surfacing technology. The Ni15 Nickle-based alloy powder is selected as deposited metal. By optimizing the welding procedure, the coating is free of crack and pore. The microstructure characteristics of deposition layer are investigated by metallographic microscope, and the microhardness of the overlay is measured by vickers hardness tester. It is found that the heat affected zone is narrow, the rate of dilution is low and the microhardness of deposition layer is about HV130 which is close to that of base metal. Furthermore, the hardness of welding surface can meet the needs of the engine.